Immunohistochemical localization of somatostatin receptor subtypes sst(1) and sst(2) in the rat retina

PURPOSE. TO investigate the distribution of somatostatin receptor subtypes sst(1) and sst(2) in the mt retina by immunohistochemistry and to character ize further the neurotransmitters of the sst(1)- and sst(2)-immunoreactive cells. METHODS. Polyclonal antibodies raised against sst(1) and sst(2) receptors w ere applied to 12-mu m cryostat sections of rat retinas fixed in paraformal dehyde. Further, immunofluorescence double labeling was performed for the s st(1) and sst(2) receptors with somatostatin, tyrosine hydroxylase (TH) and glutamate decarboxylase (GAD). RESULTS. Immunoreactivity for sst(1) was present in somatostatinergic amacr ine cells located in the inner nuclear layer (INL) and in displaced amacrin e cells in the ganglion cell layer of the retina. Also, a small number of g anglion cells were sst, immunoreactive. Immunoreactivity for sst(2) was obs erved in many medium-sized amacrine cells in the middle part of the INL, wi th a central process projecting to the sublaminae of the inner plexiform la yer. Furthermore, sst(2) immunoreactivity was found in large amacrine cells of the INL. These cells also contained TM. Inner segments of cone receptor s were stained with the sst(2) antiserum. Immunostaining for sst(2), and to a minor extent for sst(1), was found in Muller cell fibers. None of the so matostatin receptors colocalized with GAD. CONCLUSIONS. These findings suggest that the sst(1) receptor may function a s an autoreceptor on retinal somatostatinergic cells. The presence of sst(2 ) receptors on the TH-immunoreactive amacrine cells indicates an influence of somatostatin on the secretion of dopamine in mt retina.